A communication system may be provided, which includes an image data transmission apparatus and a terminal, which are connected through a network. The terminal may send a fax job request to the image data transmission apparatus, requesting the image data transmission apparatus to send image data to a specific destination via facsimile. In such case, the terminal sends the image data in the form of monochrome image such as in the form of MMR image data to reduce the data size of the image data to be transmitted through the network, for example, as described in the Japanese Patent Application Publication Nos. 2005-210531, and 2007-316854.
However, when the image data is received in the form of monochrome image, the image data transmission apparatus is not able to send the image data in the form of color image to the specific destination even when the image data transmission apparatus is capable of sending the color image data.
On the other hand, when the terminal sends the image data to the image data transmission apparatus in the form of color image, the network load of the communication system increases.